Hi all,
Here is an interesting one that I need some advice on from the collective knowledge base. Picked up an excellent condition AU-6900 recently in a known "no output" condition. So on the bench it goes and no relay click. Check offset on the emitters and all looks good, so I'm thinking protection circuit. I should point out that at this point with no relay click, the red power LED comes on solid and stays on (important for later).
Poke around in the protection circuit and all silicon seems good, so pull C603 (47uF/50v) and boom it's reading 2.5uF @ 740 ohms ESR. Replace it and relay engages and get perfect output. Now here is the issue... the power LED no longer illuminates. On diode test it has a drop of 1.44 volts so it's not open. Place a modern red LED in the connector and it doesn't light up either. Measure voltage drop across the LED and it's only 1.66v. R601 seems good at 2.2k and R602 also seems good at 120 ohm. So what am I missing here?
Here is an interesting one that I need some advice on from the collective knowledge base. Picked up an excellent condition AU-6900 recently in a known "no output" condition. So on the bench it goes and no relay click. Check offset on the emitters and all looks good, so I'm thinking protection circuit. I should point out that at this point with no relay click, the red power LED comes on solid and stays on (important for later).
Poke around in the protection circuit and all silicon seems good, so pull C603 (47uF/50v) and boom it's reading 2.5uF @ 740 ohms ESR. Replace it and relay engages and get perfect output. Now here is the issue... the power LED no longer illuminates. On diode test it has a drop of 1.44 volts so it's not open. Place a modern red LED in the connector and it doesn't light up either. Measure voltage drop across the LED and it's only 1.66v. R601 seems good at 2.2k and R602 also seems good at 120 ohm. So what am I missing here?
